1. Technical Field
The present disclosure relates to an apparatus and method of controlling black stretch, and more particularly to an apparatus and a method of controlling black stretch that enhances a contrast of a video signal when the video signal is adjusted by an offset.
2. Discussion of Related Art
A black stretch technique may be used to enhance a contrast of a video signal. The technique converts a portion of a low level video signal into a signal having a level that is lower than the low level signal, thereby enhancing the contrast between the low level signal and a high level signal. The technique analyzes a histogram of an input video signal, generates a black stretch function according to a distribution chart of the histogram, and applies the generated black stretch function to the input video signal.
FIG. 1 is a graph for describing a principle of a black stretch, and FIG. 2 is a graph for describing an offset adjustment with respect to FIG. 1. Referring to FIG. 1, black stretch may be controlled by calculating a black stretch control range, calculating a slope between a minimum value MIN and a maximum value TILT in the black stretch control range, performing black stretch processing on a video signal pertaining to the range between the minimum value MIN and the maximum value TILT in response to the slope SLOPE, and outputting 0 when the video signal has a value that is less than the minimum value.
However, as illustrated in FIG. 2, when an offset value is greater than 0, an overall output video signal is shifted in a positive direction on a Y-axis corresponding to the offset value. Therefore the contrast of the video signal is degraded because portions of the output video signal corresponding to an input video signal that are below the minimum value MIN have the offset value.
Thus, there is a need for a method and apparatus for controlling black stretch of a video signal that enhances the contrast of the video signal when the video signal is adjusted by an offset.